<html>
  <head></head>
  <body>
    <div id="app">
      <div>Ref</div>
    </div>
  </body>
  <script src="../vue002-proxy/proxy.js"></script>
  <script src="./ref.js"></script>
  <script>
    let product = reactive({ price: 5, quantity: 2 })
    let salePrice = ref(0)
    let total = 0
    effect(() => {
      total = salePrice.value * product.quantity
    })
    effect(() => {
      salePrice.value = product.price * 0.9
    })
  </script>
</html>
